JP7079204B2 - Copolymer rubber and its production method, and crosslinked rubber composition - Google Patents

Description

The present invention relates to a copolymer rubber having excellent processability and excellent tensile strength and wear resistance, and a crosslinked rubber product obtained by cross-linking the copolymer rubber.

Conjugate diene rubbers such as SBR (styrene-butadiene rubber), BR (butadiene rubber), IR (isoprene rubber) styrene-isoprene rubber, etc. have excellent wear resistance, elasticity, water resistance, molding materials, resin modifiers, etc. It is used for various purposes.

One of the main uses of this conjugated diene rubber is an automobile tire. The characteristics required for a tire include mechanical strength, wear resistance, wet grip property and the like (hereinafter, also referred to as strength and the like). Further, in recent years, tires having excellent energy-saving performance, that is, fuel efficiency (so-called "eco-tires") have been actively developed. This eco-tire is required to have low rolling resistance in addition to strength.

It is known to add a filler (reinforcing filler) such as carbon black or silica to conjugated diene rubber in order to secure the strength of the tire, but the strength of the tire is further improved and the excellent rolling resistance is obtained. As a material for imparting a tire, end-modified solution-polymerized SBR (terminal-modified S-SBR) is attracting attention. The terminal-modified S-SBR has a functional group at the molecular end of SBR, and the functional group at the molecular end interacts with the filler. This interaction improves the dispersibility of the filler in the SBR and constrains the molecular ends of the SBR to reduce motility. As a result, the hysteresis loss (internal friction) of the tire is reduced, and the rolling resistance is reduced. Taking advantage of this characteristic, eco-tires that have both strength and low rolling resistance are being developed.

For example, in Patent Document 1, an organic lithium compound is used as an initiator in a non-polar solvent, and a block copolymer composed of α-methylstyrene block and butadiene block is synthesized by living anionic polymerization, and further, if necessary, polyfunctionality. By reacting the coupling agent, S-SBR having both high temperature characteristics and rubber-like properties is obtained.
Further, Patent Document 2 discloses a star-block interpolymer having a random copolymer block of conjugated diene and a monovinyl aromatic monomer, a polyconjugated diene block, and a functional group derived from a polyfunctional lithium-based initiator. It is disclosed that it can be widely used as a rubber in the production of a tire tread having excellent properties such as reduction of rolling resistance and improvement of traction characteristics.
The techniques of Patent Documents 1 and 2 are considered to have an effect of ensuring the workability of rubber by introducing a branched structure into the rubber component. However, there is no particular device for the interaction with the filler to ensure the strength, and the contribution to the strength is not sufficient.

Further, in Patent Document 3, a rubber composition in which a predetermined amount of carbon black is blended with a blended rubber containing a plurality of diene-based rubbers has a functional group having an interaction with the carbon black at the end of the molecular chain and A rubber composition comprising a low molecular weight functional group-containing polymer having a polymer structure similar to the rubber component of the diene-based rubber is disclosed. In this rubber composition, the amount of carbon black distributed into each diene-based rubber component can be controlled by blending a small molecule compound having an interaction with carbon black into the rubber. Therefore, the characteristics of each rubber component can be effectively expressed, and it is possible to achieve both rolling characteristics and rubber characteristics that have a contradictory relationship such as wet characteristics. However, this technique is not sufficient as a contribution to strength because it blends low molecular weight compounds with rubber.
Further, in Patent Document 4, a crosslinked rubber particle containing a conjugated diene monomer unit, an aromatic vinyl monomer unit and a monomer unit having at least two polymerizable unsaturated groups, and a specific bonded structure are used. A rubber composition containing a conjugated diene / aromatic vinyl copolymerized rubber containing a conjugated diene monomer unit having is disclosed, and the crosslinked rubber particles are monomer units having a carboxylic acid group, a hydroxyl group and / or an epoxy group. It is disclosed that it may include. Since this technique has an appropriate interaction with an inorganic filler (filler) such as silica, the inorganic filler is excellent in dispersibility and processability. However, the substances disclosed as the above-mentioned monomer unit having at least two polymerizable unsaturated groups and the monomer unit having a carboxylic acid group, a hydroxyl group and / or an epoxy group are all small molecules. be. Therefore, the reactivity is excessively high, and there is a risk that gelation will proceed in the crosslinked rubber particles and the rubber composition. In addition, in this technology, it is essential to synthesize a crosslinked rubber separately from the conjugated diene / aromatic vinyl copolymerized rubber and then blend the crosslinked rubber with the conjugated diene / aromatic vinyl copolymerized rubber, which simplifies the process. From a sexual point of view, improvement is needed.
Patent Document 5 discloses a soluble polyfunctional vinyl aromatic copolymer, but does not teach that it is used in the production of copolymer rubber.

Japanese Patent Application Laid-Open No. 2003-73434 Special Table 2004-517202 Gazette Japanese Unexamined Patent Publication No. 2005-213381 WO2002 / 000779 Japanese Unexamined Patent Publication No. 2004-123873

An object of the present invention is to solve such a problem and to provide a material having workability, strength and homogeneity.

As a result of diligent studies, the present inventors have obtained the above-mentioned by using a specific polyfunctional vinyl aromatic copolymer compound having a branched structure and an interaction function with a filler as a constituent unit of the conjugated diene rubber. The present invention was completed by finding a solution to the problem.

（式中、Ｒ^１は炭素数６～３０の芳香族炭化水素基を示す。）
構造単位（ａ）の他の少なくとも一部は上記構造単位（ｄ）を構成する構造単位であり、構造単位（ａ）及び（ｂ）の総和に対するビニル基含有構造単位（ａ１）モル分率は０．０２～０．８の範囲であり、数平均分子量が３００～１０００００であることを特徴とする共重合体ゴムの製造方法である。In the present invention, in producing a copolymer rubber by copolymerizing a raw material containing a polyfunctional vinyl aromatic copolymer (A) and a conjugated diene compound (B).
The polyfunctional vinyl aromatic copolymer (A) has a structural unit (a) derived from a divinyl aromatic compound, a structural unit (b) derived from a monovinyl aromatic compound, and a structural unit (d) constituting a terminal. It contains 2 mol% or more and less than 95 mol% of the structural unit (a), and at least a part of the structural unit (a) is a vinyl group-containing structural unit (a1) represented by the following formula.

(In the formula, R ¹ represents an aromatic hydrocarbon group having 6 to 30 carbon atoms.)
At least a part of the other structural unit (a) is a structural unit constituting the structural unit (d), and the molar fraction of the vinyl group-containing structural unit (a1) with respect to the sum of the structural units (a) and (b) is It is a method for producing a copolymer rubber, which is in the range of 0.02 to 0.8 and has a number average molecular weight of 300 to 100,000.

Further, in the present invention, the polyfunctional vinyl aromatic copolymer (A) is copolymerized with a raw material containing a conjugated diene compound (B) or a conjugated diene compound (B) and an aromatic vinyl compound (C) to have a copolymer weight. A method for producing a copolymer rubber, which comprises using the above-mentioned polyfunctional vinyl aromatic copolymer as the polyfunctional vinyl aromatic copolymer (A) in producing the combined rubber.

（式中、Ｒ^２は炭素数６～３０の芳香族炭化水素基を示す。）

（式中、Ｒ^３は炭素数６～３０の芳香族炭化水素基を示し、Ｒ^４は水素原子又は炭素数６～３０の炭化水素基を示す。）The structural unit (d) constituting the terminal of the polyfunctional vinyl aromatic copolymer (A) is any of the units represented by the following (d1) to (d6). However, in the case of the unit represented by (d4) or (d5), the unit represented by (d4) or (d5) is simultaneously held.

(In the formula, R ² represents an aromatic hydrocarbon group having 6 to 30 carbon atoms.)

(In the formula, R ³ indicates an aromatic hydrocarbon group having 6 to 30 carbon atoms, and R ⁴ indicates a hydrogen atom or a hydrocarbon group having 6 to 30 carbon atoms.)

―YOZ (d3)
(In the formula, Y represents an aromatic hydrocarbon group having 6 to 52 carbon atoms substituted with an unsubstituted or hydrocarbon group having 1 to 12 carbon atoms, and Z represents an aliphatic hydrocarbon group having 1 to 30 carbon atoms. Alternatively, it indicates an aromatic hydrocarbon group having 6 to 52 carbon atoms, which is unsubstituted or substituted with a hydrocarbon group having 1 to 12 carbon atoms.)

（ここで、Ｒ^５は水素原子又は炭素数１～１８の炭化水素基を示し、Ｒ^６及びＲ^７は炭素数１～１８の炭化水素基を示し、Ｒ^８は水素原子又はメチル基を示す。）

(Here, R ⁵ indicates a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms, R ⁶ and R ⁷ indicate a hydrocarbon group having 1 to 18 carbon atoms, and R ⁸ indicates a hydrogen atom or a methyl group. .)

（ここで、Ｒ^９は１または２以上の脂環式炭化水素環を有する炭素数４～１６の炭化水素基である。）

(Here, R ⁹ is a hydrocarbon group having 1 or 2 or more alicyclic hydrocarbon rings and having 4 to 16 carbon atoms.)

Anionic polymerization is suitable as the above copolymerization method.

Further, another aspect of the present invention is characterized in that a filler is blended with the copolymer rubber obtained by the above-mentioned method for producing a copolymer rubber and crosslinked by vulcanization to obtain a rubber composition. This is a method for producing a rubber composition.

Further, another aspect of the present invention is a structural unit (A1) of a polyfunctional vinyl aromatic copolymer and a structural unit (B1) of a conjugated diene compound, or a structural unit (B1) of a conjugated diene compound and an aromatic vinyl. A copolymer rubber containing a structural unit (C1) of a compound.
It contains 0.001 to 6% by weight of the structural unit (A1), 29 to 99.999% by weight of the structural unit (B1), and 0 to 70% by weight of the structural unit (C1).
The structural unit (A1) contains a structural unit (a) derived from a divinyl aromatic compound, a structural unit (b) derived from a monovinyl aromatic compound, and a structural unit (d) constituting a terminal, and is a structural unit ( It contains 2 mol% or more and less than 95 mol% of a), and at least a part of the structural unit (a) is a vinyl group-containing structural unit (a1) represented by the above formula, and at least the other structural unit (a). Some of them are structural units constituting the structural unit (d), and the molar fraction of the vinyl group-containing structural unit (a1) with respect to the sum of the structural units (a) and (b) is in the range of 0.02 to 0.8. It is a copolymer rubber characterized by being.

The number average molecular weight of the structural unit (A1) in the above-mentioned copolymer rubber is preferably 300 to 100,000. The structural unit (d) constituting the end of the copolymer rubber may be any of the units represented by the above (d1) to (d6). However, in the case of the unit represented by (d4) or (d5), the unit represented by (d4) or (d5) is simultaneously held.

Another aspect of the present invention is a crosslinked rubber composition containing the above-mentioned copolymer rubber and a filler, wherein the copolymer rubber has a crosslinked structure. Further, it is a polyfunctional vinyl aromatic copolymer characterized by being used in the above-mentioned copolymer rubber and crosslinked rubber composition.

Since the copolymer rubber of the present invention has a structural unit of a specific polyfunctional vinyl aromatic copolymer having a branched structure and a function of interacting with a filler, it has both processability and strength. Furthermore, gel-like substances are difficult to form and become homogeneous, and can be applied to molding materials, resin modifiers, and the like.
Further, the crosslinked rubber composition in which the copolymer rubber contains a filler and is crosslinked is excellent in the dispersibility of the filler, and therefore excellent in mechanical strength and wear resistance.

In the method for producing a copolymer rubber of the present invention, a raw material containing a polyfunctional vinyl aromatic copolymer (A), a conjugated diene compound (B) and, if necessary, an aromatic vinyl compound (C) is used as a raw material. Copolymerize.

The polyfunctional vinyl aromatic copolymer (A) is obtained by copolymerizing a divinyl aromatic compound and a monovinyl aromatic compound, and is preferably solvent-soluble. For example, it may be soluble in toluene, xylene, tetrahydrofuran, dichloroethane or chloroform.
The number average molecular weight Mn of the polyfunctional vinyl aromatic copolymer (A) is 300 to 100,000, preferably 500 to 5,000. The molecular weight distribution Mw / Mn is preferably in the range of 3 to 20.

The divinyl aromatic compound gives the structural unit (a), and the monovinyl aromatic compound gives the structural unit (b). Since the divinyl aromatic compound has a plurality of vinyl groups, it is crosslinked to give a branched structure, but the degree of crosslinking is controlled to the extent that it exhibits solubility. The structural unit having an unreacted vinyl group becomes the structural unit (a) or the structural unit (d1) as the structural unit (d) constituting the terminal, and gives a polyfunctional structure having a plurality of vinyl groups.

The polyfunctional vinyl aromatic copolymer (A) contains the structural unit (a) in an amount of 2 mol% or more and less than 95 mol%. It preferably contains 5 to 90 mol%, more preferably 10 to 90 mol%, and particularly preferably 15 to 85 mol%.
Then, a part of the structural unit (a) may contain 1 mol% or more of the structural unit (a1), preferably 2 to 80 mol%, more preferably 5 to 70 mol%, still more preferably. Is 10 to 60 mol%, particularly preferably 15 to 50 mol%.
Further, a part of the structural unit (a) is contained as a structural unit (d1) in the structural unit (d) constituting the terminal, and the amount thereof is 0.7 or more per molecule, preferably 1.0. The number is preferably 1.5 or more, more preferably 1.5 or more.
In the above calculation, the structural unit (a) includes the structural unit (a1) and the structural unit (d1).
Further, it is preferable to have an average of 2.1 or more, preferably 2.5 or more, and more preferably 3 or more of the terminal structural units (d) per molecule.

The polyfunctional vinyl aromatic copolymer (A) contains the structural unit (b) in an amount of 5 mol% or more and less than 98 mol%. It preferably contains 10 to 95 mol%, more preferably 10 to 90 mol%, and particularly preferably 15 to 85 mol%. A part of the structural unit (b) may be a terminal structural unit (d). This structural unit is called a structural unit (d2).

The structural unit (a) derived from the divinyl aromatic compound contains a vinyl group as a cross-linking component for developing heat resistance and rigidity, while the structural unit (b) derived from the monovinyl aromatic compound is a curing reaction. Since it does not have a vinyl group involved in, it gives flexibility and solubility.

The terminal structural unit (d) may be composed of a part of the structural unit (a) and the structural unit (b), and the monomers other than the divinyl aromatic compound and the monovinyl aromatic compound (G). ) May be used, and a part or all of the structural unit resulting from this may be used as the terminal structural unit (d). This structural unit is called a structural unit (d3).

The polyfunctional vinyl aromatic copolymer (A) can be obtained by the method described in Patent Document 5 and the like. For example, it can be obtained by polymerizing a monomer containing a divinyl aromatic compound, a monovinyl aromatic compound and, if necessary, another monomer (G) at a temperature of 20 to 120 ° C. in a uniform solvent dissolved in a solvent.

As examples of the divinyl aromatic compound, divinylbenzene (including each isomer), divinylnaphthalene (including each isomer), and divinylbiphenyl (including each isomer) are preferably used, but are limited thereto. is not. In addition, these can be used alone or in combination of two or more. From the viewpoint of moldability, divinylbenzene (m-form, p-form or a mixture thereof) is more preferable.

Examples of monovinyl aromatic compounds include vinyl aromatic compounds such as styrene, vinylnaphthalene and vinylbiphenyl, o-methylstyrene, m-methylstyrene, p-methylstyrene, o, p-dimethylstyrene and o-ethylvinylbenzene. , M-Ethylvinylbenzene, p-Ethylvinylbenzene and other nuclear alkyl substituted vinyl aromatic compounds, etc., but styrene, ethylvinylbenzene (including each isomer), ethylvinyl biphenyl (including each isomer), And ethylvinylnaphthalene (including each isomer) are preferable.

Examples of other monomers (G) used as necessary include divinyl aromatic compounds, monomers copolymerizable with monovinyl aromatic compounds, terminal modifiers and chain transfer agents that give desired terminal groups, and the like. Be done.

As the structural unit (d) constituting the terminal of the polyfunctional vinyl aromatic copolymer (A), the units represented by the above formulas (d1) to (d6) are preferable. However, in the case of the unit represented by the formula (d4) or the formula (d5), the unit represented by the formula (d4) and the formula (d5) is simultaneously possessed.

In formula (d1), R ² represents an aromatic hydrocarbon group having 6 to 30 carbon atoms. The formula (d1) can be derived from a divinyl aromatic compound as a monomer. Specifically, it is divinylbenzene, divinylnaphthalene, divinylanthracene, divinylphenanslenne, divinylbiphenyl, divinyltriphenyl and the like. Divinylbenzene, divinylnaphthalene, and divinylbiphenyl are preferable because the polyfunctional vinyl aromatic copolymer (A) is easy to handle in rubber solution polymerization and has excellent interaction with fillers.
In the formula (d2), R ³ represents an aromatic hydrocarbon group having 6 to 30 carbon atoms, and R ⁴ represents a hydrogen atom or a hydrocarbon group having 6 to 30 carbon atoms. Formula (d2) can be derived from a monovinyl aromatic compound as a monomer. Specifically, vinyl toluene, ethyl vinylbenzene, n-propylstyrene, isopropylstyrene, butylstyrene, methylvinylnaphthalene, ethylvinylnaphthalene, methylvinylphenanthrene, ethylvinylphenanthrene, methylvinylanthracene, ethylvinylanthracene. , Methylvinylbiphenyl, ethylvinylbiphenyl, methylvinyltriphenyl, ethylvinyltriphenyl and the like. Preferably, R ³ is a phenyl group, a naphthyl group, a biphenylyl group, and R ⁴ because the polyfunctional vinyl aromatic copolymer (A) is easy to handle in rubber solution polymerization and has excellent interaction with a filler. Is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Specifically, vinyl toluene, ethyl vinylbenzene, n-propylstyrene, isopropylstyrene, n-butylstyrene, isobutylstyrene, sec-butylstyrene, t-butylstyrene, methylvinylnaphthalene, ethylvinylnaphthalene, methylvinylbiphenyl, Ethylvinylbiphenyl, etc. may be mentioned. More preferably, it is vinyltoluene, ethylvinylbenzene, isopropylstyrene, t-butylstyrene.

In formula (d3), Y represents an aromatic hydrocarbon group having 6 to 52 carbon atoms substituted with an unsubstituted or hydrocarbon group having 1 to 12 carbon atoms, and Z represents an aliphatic hydrocarbon having 1 to 30 carbon atoms. Indicates an aromatic hydrocarbon group having 6 to 52 carbon atoms, which is a group or an unsubstituted or substituted hydrocarbon group having 1 to 12 carbon atoms. The formula (d3) can be derived from anisole, ethoxybenzene, propoxybenzene, butoxybenzene, methoxynaphthalene, methoxybiphenyl, biphenyl ether used as the monomers (G). Anisole, butoxybenzene, and methoxynaphthalene are preferable because the polyfunctional vinyl aromatic copolymer (A) is easy to handle in rubber solution polymerization and has excellent interaction with a filler.

In the formulas (d4) and (d5), R ⁵ indicates a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms, R ⁶ and R ⁷ indicate a hydrocarbon group having 1 to 18 carbon atoms, and R ⁶ and R ⁷ may be bonded to each other to form a ring. When R ⁶ and R ⁷ form a ring with each other, the total number of carbon atoms of R ⁶ and R ⁷ is 2 to 36. Further, R ⁸ represents a hydrogen atom or a methyl group. Formulas (d4) and (d5) are used as monomers (G), methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, (. N-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, t-butyl (meth) acrylate, etc., aliphatic (meth) acrylate of 2-ethylhexyl (meth) acrylate , (Meta) acrylate having an alicyclic such as (meth) cyclopentyl acrylate, (meth) cycloxyl acrylate, or (meth) acrylate having an aromatic ring such as phenyl (meth) acrylate, naphthyl (meth) acrylate. And so on. Preferably, since the polyfunctional vinyl aromatic copolymer (A) is easy to handle in rubber solution polymerization and has excellent interaction with a filler, isopropyl (meth) acrylate, isobutyl (meth) acrylate, (meth). ) S-butyl acrylate and t-butyl (meth) acrylate.

In formula (d6), R ⁹ is a hydrocarbon group having 1 or 2 or more alicyclic hydrocarbon rings and having 4 to 6 carbon atoms. R ⁹ binds to the molecular chain via an adjacent carbon-carbon double bond. The formula (d6) can be derived from cyclopentene, cyclohexene, norbornene, dicyclopenta-monoene and the like used as the monomers (G). Norbornene is preferable because it is easy to handle in rubber solution polymerization of the polyfunctional vinyl aromatic copolymer (A) and is excellent in interaction with a filler.

An acid catalyst or a Lewis acid catalyst is suitable as a catalyst for copolymerizing a divinyl aromatic compound or a monovinyl aromatic compound and a monomer containing another monomer (G), if necessary.
As the acid catalyst, a sulfonic acid catalyst such as an alkyl sulfonic acid or a toluene sulfonic acid can be used. The amount used is 0.1 to 10 mol with respect to a total of 100 mol of all the monomer components.

The Lewis acid catalyst can be used without particular limitation as long as it is a compound composed of a metal ion (acid) and a ligand (base) and can receive an electron pair. Among the Lewis acid catalysts, metal fluorides or complexes thereof are preferable from the viewpoint of thermal decomposition resistance of the obtained copolymer, and in particular, B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Ti, A divalent to hexavalent metal fluoride such as W, Zn, Fe and V or a complex thereof is preferable. These catalysts can be used alone or in combination of two or more. From the viewpoint of controlling the molecular weight and molecular weight distribution of the obtained copolymer and the polymerization activity, an ether complex of boron trifluoride is most preferably used. Here, examples of the ether of the ether complex include diethyl ether and dimethyl ether.
As the Lewis acid catalyst, the Lewis acid catalyst is preferably used in the range of 0.001 to 100 mol, more preferably 0.01 to 50 mol, based on 100 mol of the total monomer components. Most preferably 0.1 to 10 mol.
Further, if desired, one or more Lewis base compounds can be used as a co-catalyst. Specific examples of the Lewis basic compound include an ester compound such as ethyl acetate, a thioester compound such as methyl mercaptopropionic acid, a ketone compound such as methyl ethyl ketone, an amine compound such as methyl amine, an ether compound of diethyl ether, and diethyl. There are thioether-based compounds such as sulfide, and phosphine-based compounds such as tripropylphosphine and tributylphosphine.

The polymerization reaction is carried out, for example, at 20 to 120 ° C., preferably 40 to 100 ° C. in a uniform solvent in which the above-mentioned monomer and an acid catalyst or a Lewis acid catalyst are dissolved in an organic solvent having a dielectric constant of 2.0 to 15.0. A method of cation copolymerization is suitable.
As the organic solvent, toluene, xylene, n-hexane, cyclohexane, methylcyclohexane or ethylcyclohexane is particularly preferable from the viewpoint of the balance between polymerization activity and solubility.

The method for recovering the polyfunctional vinyl aromatic copolymer after the polymerization reaction is stopped is not particularly limited, and for example, a commonly used method such as a heat concentration method, a steam stripping method, or precipitation in a poor solvent may be used.

A copolymer rubber is produced by copolymerizing the polyfunctional vinyl aromatic copolymer (A) and the conjugated diene compound (B) with a raw material containing an aromatic vinyl compound (C), if necessary. When the aromatic vinyl compound (C) is not used, a diene rubber such as butadiene rubber or isoprene rubber can be obtained, and by using the aromatic vinyl compound (C), a covalent rubber such as SBR can be obtained. Obtainable.

A method for producing a copolymer rubber by copolymerizing a conjugated diene compound (B) or a raw material containing the same and an aromatic vinyl compound (C) is one of the raw materials of a polyfunctional vinyl aromatic copolymer (A). In addition to the above, the methods described in Patent Documents 1 to 4 can be adopted.

Examples of the conjugated diene compound (B) include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, and 1,3-hexadiene. Etc. can be used alone or in combination of two or more, but among these, 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene are preferable.

Examples of the aromatic vinyl compound include styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, 2,4,6-trimethylstyrene, and tert-butoxy. Dimethylsilylstyrene, isopropoxydimethylsilylstyrene and the like can be used alone or in combination of two or more, but among these, styrene is preferable.

When 1,3-butadiene is used as the conjugated diene compound (B) and styrene is used as the aromatic vinyl compound, so-called styrene-butadiene rubber (SBR) can be obtained. Further, when styrene is not used as the aromatic vinyl compound and 1,3-butadiene is used as the conjugated diene compound (B), so-called butadiene rubber (BR) can be obtained. When isoprene is used as the conjugated diene compound (B) and there is no structural unit of the aromatic vinyl compound (C), it becomes isoprene rubber (IR). Among them, having a styrene-butadiene rubber (SBR) structure is particularly preferable because it has excellent wear resistance, heat resistance, and aging resistance.

The method for producing a copolymer rubber by copolymerizing a raw material containing these is not limited, but anionic polymerization in a hydrocarbon solvent is preferable.
For example, a method of subjecting a polyfunctional vinyl aromatic copolymer, a conjugated diene compound, or a living anion polymerization of these with an aromatic vinyl compound in a hydrocarbon solvent using an organic alkali metal compound as an initiator, or a conjugated diene compound. There is also a multi-step reaction method in which a polyfunctional vinyl aromatic copolymer is added after the living anionic polymerization of the aromatic vinyl compound and the reaction is carried out. Further, if necessary, the terminal may be terminal-modified with a polymerization terminator having a functional group.

Specific examples of the hydrocarbon solvent used in the above method include propane, n-butene, isobutane, n-pentane, isopentane, n-hexane, cyclohexane, propene, 1-butene, isobutane, and trans-2-. Butene, cis-2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene, ethylbenzene, heptane, cyclopentane, methylcyclopentane, methylcyclohexane, 1-pentene, 2- Examples include pentane and cyclohexene.

Examples of the organic alkali metal used as an initiator include methyllithium, ethyllithium, n-propyllithium, iso-propyllithium, n-butyllithium, sec-butyllithium, tert-octyllithium, n-decyllithium, and phenyl. Examples thereof include lithium, 2-naphthyllithium, 2-butyl-phenyllithium, 4-phenyl-butyllithium, cyclohexyllithium, and reaction products of diisopropenylbenzene and butyllithium.

The method of using the polyfunctional vinyl aromatic copolymer (A) in the polymerization is not particularly limited, and for example, a method of starting the polymerization in coexistence with the conjugated diene compound (B) and, if necessary, the aromatic vinyl compound (C). , (A) and the polymerization initiator, followed by (B) and, if necessary, the method of adding the aromatic vinyl compound (C), the conjugated diene compound (B) and, if necessary, the aromatic vinyl compound (C). A method of adding a polyfunctional vinyl aromatic copolymer (A) during the polymerization to give the rubber molecule a branched structure, a conjugated diene compound (B) and, if necessary, a polyfunctional vinyl compound (C) at the end of polymerization. Examples thereof include a method of adding a vinyl aromatic copolymer (A) to couple rubber molecules.

The weight average molecular weight of the copolymer rubber is preferably in the range of 100,000 to 500,000. The reaction can be terminated by adding alkanol or the like, and the solvent can be removed to obtain a copolymer rubber.

The ratio of the polyfunctional vinyl aromatic copolymer (A), the conjugated diene compound (B) and the aromatic vinyl compound (C) is preferably in the following range.
The polyfunctional vinyl aromatic copolymer (A) is 0.001 to 6% by weight, preferably 0.005 to 3% by weight, more preferably 0.01 to 2% by weight, and the conjugated diene compound (B). Is 94 to 99.999% by weight, and the aromatic vinyl compound (C) is 0 to 70% by weight.
When the aromatic vinyl compound (C) is used, the polyfunctional vinyl aromatic copolymer (A) is in the same range as described above, and the conjugated diene compound (B) is 50 to 97% by weight, preferably 55. It is about 90% by weight, and the aromatic vinyl compound (C) is 2 to 50% by weight, preferably 5 to 45% by weight.
More preferably, the polyfunctional vinyl aromatic copolymer (A) is 0.01 to 23% by weight, still more preferably 0.1 to 1% by weight. The conjugated diene compound (B) is 50 to 97% by weight, more preferably 55 to 90% by weight. The aromatic vinyl compound (C) is preferably in the range of 2 to 49% by weight, more preferably 5 to 44% by weight.

（式中、Ｒ^１は炭素数６～３０の芳香族炭化水素基を示す。）
構造単位（ａ）の他の少なくとも一部は上記構造単位（ｄ）を構成する構造単位であり、構造単位（ａ）及び（ｂ）の総和に対するビニル基含有構造単位（ａ１）モル分率は０．０２～０．８の範囲であり、数平均分子量が３００～１０００００である。
好ましい範囲は、上記原料の使用割合と同様な割合となることがよい。The content ratio of the structural unit (A1) of the polyfunctional vinyl aromatic copolymer, the structural unit (B1) of the conjugated diene compound, and the structural unit (C1) of the aromatic vinyl compound in the copolymer rubber of the present invention is the structure. The unit (A1) is 0.001 to 6% by weight, the structural unit (B1) is 29 to 99.999% by weight, and the structural unit (C1) is 0 to 70% by weight.
It contains a structural unit (a) derived from a divinyl aromatic compound, a structural unit (b) derived from a monovinyl aromatic compound, and a structural unit (d) constituting a terminal, and the structural unit (a) is 2 mol% or more. It contains less than 95 mol%, and at least a part of the structural unit (a) is a vinyl group-containing structural unit (a1) represented by the following formula.

(In the formula, R ¹ represents an aromatic hydrocarbon group having 6 to 30 carbon atoms.)
At least a part of the other structural unit (a) is a structural unit constituting the structural unit (d), and the molar fraction of the vinyl group-containing structural unit (a1) with respect to the sum of the structural units (a) and (b) is It ranges from 0.02 to 0.8 and has a number average molecular weight of 300 to 100,000.
The preferable range may be a ratio similar to the ratio of the raw materials used.

The crosslinked rubber composition of the present invention can be obtained by blending a filler or a crosslinking agent with the above-mentioned copolymer rubber to prepare a rubber composition, and crosslinking this rubber composition by vulcanization. Examples of the filler include carbon black and silica. Especially excellent in interaction with carbon black.

As the carbon black contained as the filler, carbon black of each grade such as SRF, GPF, FEF, HAF, ISAF, and SAF can be used. Among these, HAF, ISAF, and SAF are preferable because a rubber elastic body having excellent wear resistance can be obtained.
The silica may be in the form of particles generally used as a filler, but the primary particle diameter is preferably 50 nm or less. Specific examples of such silica include hydrous silicic acid, anhydrous silicic acid, calcium silicate, aluminum silicate and the like.

The content ratio of the filler is preferably 10 to 120 parts by mass with respect to 100 parts by weight of the total rubber component including the copolymer rubber, and 55 to 100 parts by weight from the viewpoint of reinforcing property and the effect of improving various physical properties. It is more preferably a part.

The cross-linking agent contained in the rubber composition is not particularly limited, such as cross-linking with sulfur and cross-linking with peroxide, but sulfur is usually used. The content ratio of the cross-linking agent is preferably 0.1 to 5 parts by weight, more preferably 1 to 3 parts by weight, based on 100 parts by weight of the total rubber component.

In the above rubber composition, in addition to the above components, if necessary, a silane coupling agent, a paraffin oil, a naphthen oil, a rubber compound oil such as an aroma oil, a wax, an antiaging agent, and stearic acid (addition). It may contain a vulcanization aid and a processing aid), zinc oxide, a vulcanization accelerator and the like.

The rubber composition can be prepared by kneading each component using, for example, a kneader such as a plast mill, a Banbury mixer, a roll, or an internal mixer. Specifically, among the above-mentioned components, components other than the cross-linking agent and the vulcanization accelerator may be kneaded, and then the cross-linking agent and the vulcanization accelerator may be added to the obtained kneaded product and further kneaded. preferable.

Since the rubber composition of the present invention is excellent in mechanical strength and wear resistance, it is suitable as a rubber composition for obtaining a tread of a tire such as a fuel-efficient tire, a large tire, a high-performance tire, or a sidewall member. .. Further, it can be suitably used for rubber belts, rubber hoses, materials for footwear and the like.

The crosslinked rubber composition of the present invention is obtained by crosslinking the above rubber composition. For example, a tire is manufactured by extruding the above rubber composition according to the shape of the tire (specifically, the shape of the tread), molding the tire, and heating and pressurizing the rubber composition in a vulcanizer. However, by assembling this tread and other parts, the desired tire can be manufactured.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. Unless otherwise specified, the parts in each example are all parts by weight, and the evaluation of each physical property was performed by the method shown below.

1) Molecular weight and molecular weight distribution For the measurement of molecular weight and molecular weight distribution, GPC (manufactured by Tosoh, HLC-8220GPC) is used, and the solvent is tetrahydrofuran (THF), the flow rate is 1.0 ml / min, the column temperature is 38 ° C., and the calibration curve is monodisperse polystyrene. It was done using a wire.

2) Structure of polyfunctional vinyl aromatic copolymer It was determined by ¹³ C-NMR and ¹ H-NMR analysis using a JNM-LA600 type nuclear magnetic resonance spectrometer manufactured by JEOL Ltd. Chloroform-d ₁ was used as the solvent and the resonance line of tetramethylsilane was used as the internal standard.

3) Analysis of terminal groups The terminal groups are calculated based on the number average molecular weight obtained from the above GPC measurement and the total amount of monomers obtained from the results of ¹³ C-NMR and ¹ H-NMR measurements and gas chromatograph (GC) analysis. From the amount of the derivative used for introducing the polyfunctional vinyl aromatic copolymer, the number of terminal groups contained in one molecule of the polyfunctional vinyl aromatic copolymer was calculated. In Synthesis Example 1, the terminal group is derived from a divinyl aromatic compound or a monovinyl aromatic compound. The calculation of the terminal group is based on the data on the total amount of each structural unit introduced into the copolymer obtained by GC analysis in addition to the measurement results of ¹³ C-NMR and ¹ H-NMR. The introduction amount of the structural unit is calculated, and it is contained in one molecule of the polyfunctional vinyl aromatic copolymer from the introduction amount of the specific structural unit introduced at the terminal and the number average molecular weight obtained from the above GPC measurement. The number of terminal groups for a particular structural unit was calculated.

4) Mooney viscosity (ML (1 + 4) 100 ° C.)
It was determined according to JIS K6300-1 with an L-shaped rotor, preheating for 1 minute, a rotor operating time of 4 minutes, and a temperature of 100 ° C.

5) Confirmation of gel-like substance The copolymer rubber was dissolved in 5 times the weight of cyclohexane, the solution was filtered, and the presence or absence of residue on the filter was visually confirmed. If there was a residue, it was judged that there was a gel-like substance.

6) Tensile strength 300% modulus was measured by the tensile test method of JIS K6251, and the measured value of the crosslinked rubber obtained in Comparative Example 1 was set as 100 and indexed. The larger the exponential value, the better the tensile strength.

7) Abrasion resistance Using a method using a Ramborn type abrasion tester compliant with JIS K6264, the amount of wear with a slip ratio of 30% was measured, and the measured value of the crosslinked rubber obtained in Comparative Example 1 was set to 100. Indexed. The larger the index value, the better the wear resistance.

Synthesis example 1
DVB-810 (manufactured by Nippon Steel & Sumitomo Metal Corporation, content of divinylbenzene component 81.0 wt%) 320.5 mL (divinylbenzene component 1.82 mol, ethylvinylbenzene component 0.43 mol), n-butyl acetate 0.28 mol (36.9 mL), 140 mL of toluene was placed in a 1.0 L reactor, and a solution of 40 mmol of methanesulfonic acid at 70 ° C. in 0.12 mol (15.7 mL) of n-butyl acetate was added. And reacted for 6 hours. After stopping the polymerization solution with calcium hydroxide, filtration was performed using activated alumina as a filtration aid. Then, it was devolatile under reduced pressure at 60 ° C. to obtain 22.6 g of a soluble polyfunctional vinyl aromatic copolymer (copolymer X1).
The obtained copolymer X1 had Mn of 1085, Mw of 12400, and Mw / Mn of 11.4. By GC analysis, GPC measurement, FT-IR, ¹³ C-NMR and ¹ H-NMR analysis, the copolymer X is the following vinyl group-containing structural unit (a1) and terminal group derived from the divinyl aromatic compound (a). It was confirmed that d1) has the following terminal group (d2) derived from the monovinyl aromatic compound (b).

（＊は、共重合体Ｘ１の主鎖との結合部分である。）

(* Is a bonding portion of the copolymer X1 with the main chain.)

The number of terminal structural units (d1) per molecule was 7.7. Further, the copolymer X1 contained 84.0 mol% and 16.0 mol%, respectively, of the divinylbenzene component and the structural unit derived from ethylvinylbenzene with respect to the total of both. The mole fraction of the vinyl group-containing structural unit (a1) with respect to the entire structure was 0.39.
In addition, the copolymer X1 was soluble in toluene, xylene, THF, dichloroethane, dichloromethane, and chloroform, and no gel formation was observed.

Synthesis example 2
DVB-810 276.4 mL, toluene 86.2 mL, and anisole 93.74 mL were placed in a 1.0 L reactor, and a solution of 10 mmol methanesulfonic acid dissolved in 2 mL of toluene at 50 ° C. was added, and 4 Copolymer X2 was obtained in the same manner as in Synthesis Example 1 except for the time reaction.
The obtained copolymer X2 had Mn of 1000, Mw of 18800, and Mw / Mn of 18.8. By GC analysis, GPC measurement, FT-IR, 13C-NMR and 1H-NMR analysis, the copolymer X2 is the same vinyl group-containing structural unit (a1) as in Synthesis Example 1 derived from the divinyl aromatic compound (a). , And the following terminal group (d3) derived from anisole.

（＊は、共重合体主鎖との結合部分である。）

(* Is the bonding portion with the copolymer main chain.)

The copolymer X2 contains 64.0 mol% of the structural unit (a) derived from the divinylbenzene component with respect to the entire structure, and contains an average of 2.0 terminal structural groups (d3) derived from anisole per molecule. Was. The mole fraction of the vinyl group-containing structural unit (a1) with respect to the entire structure was 0.12. In addition, it was soluble in toluene, xylene, THF, dichloroethane, dichloromethane, and chloroform, and no gel formation was observed.

Synthesis example 3
DVB-810 300 mL, toluene 177.6 mL, t-butyl methacrylate 145.6 mL, a solution of 10 mmol methanesulfonic acid dissolved in 2 mL of toluene at 60 ° C. was added and reacted for 4 hours. Copolymer X3 was obtained in the same manner as in 1.
The obtained copolymer X3 had Mn of 2190, Mw of 13600, and Mw / Mn of 7.2. By GC analysis, GPC measurement, FT-IR, 13C-NMR and 1H-NMR analysis, the copolymer X3 is the same vinyl group-containing structural unit (a1) as in Synthesis Example 1 derived from the divinyl aromatic compound (a). , And a terminal group (d4) (R ⁵ , R ⁶ , R ⁷ = CH ₃ ) and a terminal group (d 5) (R ⁸ = CH ₃ ) derived from t-butyl methacrylate.

The copolymer X3 contains 71 mol% of the structural unit (a) derived from the divinylbenzene component and the terminal structural groups (d4) and (d5) derived from t-butyl methacrylate on average for the entire structure. It contained 7 pieces. The mole fraction of the vinyl group-containing structural unit (a1) with respect to the entire structure was 0.53.
In addition, the copolymer X3 was soluble in toluene, xylene, THF, dichloroethane, dichloromethane, and chloroform, and no gel formation was observed.

Example 1
245 g of cyclohexane, 2.5 g of THF, 10 g of styrene, 40 g of 1,3-butadiene, and 0.015 g of the copolymer obtained in Synthesis Example 1 were added to an autoclave reactor having an internal volume of 0.5 liters substituted with nitrogen. .. At 25 ° C., 5 g of a cyclohexane solution containing 50 mg of sec-butyllithium was added to initiate polymerization. The temperature of the reaction solution increased due to the heat of polymerization, and the maximum temperature reached 85 ° C.
After confirming that the polymerization conversion rate reached 99%, 50 mg of isopropanol was added to terminate the polymerization, and 2,6-di-tert-butyl-p-cresol (BHT) was added to the reaction solution. Then, the solvent was removed by steam stripping to obtain a copolymer rubber A. Table 1 shows the physical characteristics of the obtained copolymer rubber A.

Example 2
The copolymer rubber A, process oil, carbon black, zinc oxide, stearic acid and an antiaging agent were kneaded at 155 ° C. and 60 rpm for 4 minutes using a laboplast mill.
Sulfur and a vulcanization accelerator were added to the kneaded product obtained by the above kneading, and the mixture was kneaded at 70 ° C. and 60 rpm for 1 minute using a laboplast mill, and vulcanized to obtain crosslinked rubber A.
Table 2 shows the mixing ratio of each additive. Table 3 shows the physical characteristics of the crosslinked rubber A.

Examples 3-4
The copolymer rubber C and the copolymer rubber D were obtained in the same manner as in Example 1 except that the copolymer X2 and the copolymer X3 were used instead of the copolymer X1. The obtained physical properties are shown in Table 1.

Examples 5-6
Crosslinked rubber C and crosslinked rubber D were obtained in the same manner as in Example 2 except that the copolymer rubber C and the copolymer rubber D were used instead of the copolymer rubber A. The obtained physical properties are shown in Table 3.

Comparative Example 1
In Example 1, the copolymer rubber B was used in the same manner as in Example 1 except that 0.005 g of DVB-810 was used in place of the copolymer X1 synthesized in Synthesis Example 1 in terms of divinylbenzene. Got Table 1 shows the physical characteristics of the obtained copolymer rubber B.

Comparative Example 2
Further, using the copolymer rubber B, the crosslinked rubber B was obtained by the same method as in Example 1 and the blending ratio of each additive. Table 3 shows the physical characteristics of the crosslinked rubber B.

The additives used in Table 2 are as follows.
Rubber compound oil: Idemitsu Kosan Dyna Process Oil AC-12
Sulfur: Tsurumi Kagaku Kogyo Co., Ltd. Powdered sulfur Zinc oxide: Mitsui Mining & Smelting Co., Ltd. Zinc Hua No. 1 Stearic acid: Nikko Carbon Black: Shin Nikka Carbon Co., Ltd. Niteron # 300
Vulcanization accelerator: N-tert-butylbenzothiazole-2-sulfenamide Anti-aging agent: Noxeller NS manufactured by Ouchi Shinko Kagaku Kogyo
Blended rubber

From Tables 1 and 3, the rubber composition of the present invention provides the same processability as the case of using divinylbenzene, which is a known branching agent, and is a vulcanized rubber containing carbon black, and has tensile strength and abrasion resistance. It turns out that it is excellent in sex.

The copolymer rubber of the present invention is useful as an elastomer material for tires (particularly tire treads), seismic isolation rubbers, rubber hoses, rubber rollers, footwear materials and the like.

Claims (7)

In producing a copolymer rubber by copolymerizing a raw material containing a polyfunctional vinyl aromatic copolymer (A) and a conjugated diene compound (B).
The proportion of the polyfunctional vinyl aromatic copolymer (A) used is 0.001 to 6% by weight.
The polyfunctional vinyl aromatic copolymer (A) has a structural unit (a) derived from a divinyl aromatic compound, a structural unit (b) derived from a monovinyl aromatic compound, and a structural unit (d) constituting a terminal. Contains,
When the structural unit (d) constituting the terminal is any of the structural units represented by the following (d1) to (d6) (however, when the unit is represented by (d4) or (d5), (d4). Alternatively, it also has a unit represented by (d5)), a structural unit derived from a monomer copolymerizable with a divinyl aromatic compound or a monovinyl compound, or a structural unit derived from a terminal modifier or a chain transfer agent.

(In the formula, R ² represents an aromatic hydrocarbon group having 6 to 30 carbon atoms.)

(In the formula, R ³ indicates an aromatic hydrocarbon group having 6 to 30 carbon atoms, and R ⁴ indicates a hydrogen atom or a hydrocarbon group having 6 to 30 carbon atoms.)
―YOZ (d3)
(In the formula, Y represents an aromatic hydrocarbon group having 6 to 52 carbon atoms substituted with an unsubstituted or hydrocarbon group having 1 to 12 carbon atoms, and Z represents an aliphatic hydrocarbon group having 1 to 30 carbon atoms. Alternatively, it indicates an aromatic hydrocarbon group having 6 to 52 carbon atoms, which is unsubstituted or substituted with a hydrocarbon group having 1 to 12 carbon atoms.)

(Here, R ⁵ indicates a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms, R ⁶ and R ⁷ indicate a hydrocarbon group having 1 to 18 carbon atoms, and R ⁸ indicates a hydrogen atom or a methyl group. .)

(Here, R ⁹ is a hydrocarbon group having 1 or 2 or more alicyclic hydrocarbon rings and having 4 to 16 carbon atoms.)
The structural unit (a) is contained in an amount of 2 mol% or more and less than 95 mol%, and at least a part of the structural unit (a) is a vinyl group-containing structural unit (a1) represented by the following formula.

(In the formula, R ¹ represents an aromatic hydrocarbon group having 6 to 30 carbon atoms.)
At least a part of the other structural unit (a) is a structural unit constituting the structural unit (d), and the molar fraction of the vinyl group-containing structural unit (a1) with respect to the sum of the structural units (a) and (b) is A method for producing a copolymer rubber, which is in the range of 0.02 to 0.8, has a number average molecular weight of 300 to 100,000, and is solvent-soluble. The first aspect of the present invention is to produce a copolymer rubber by copolymerizing a raw material containing a polyfunctional vinyl aromatic copolymer (A), a conjugated diene compound (B) and an aromatic vinyl compound (C). The method for producing a copolymer rubber according to the above. The method for producing a copolymer rubber according to claim 1 or 2 , wherein the copolymerization is carried out by anionic polymerization. Crosslinking characterized in that a filler is blended with the copolymer rubber obtained by the method for producing a copolymer rubber according to any one of claims 1 to 3 and crosslinked by vulcanization to obtain a rubber composition. A method for producing a rubber composition. A co-containing a structural unit (A1) of a polyfunctional vinyl aromatic copolymer, a structural unit (B1) of a conjugated diene compound, a structural unit (B1) of a conjugated diene compound, and a structural unit (C1) of an aromatic vinyl compound. It ’s a polymer rubber,
It contains 0.001 to 6% by weight of the structural unit (A1), 29 to 99.999% by weight of the structural unit (B1), and 0 to 70% by weight of the structural unit (C1).
The structural unit (A1) is
It contains a structural unit (a) derived from a divinyl aromatic compound, a structural unit (b) derived from a monovinyl aromatic compound, and a structural unit (d) constituting a terminal.
When the structural unit (d) constituting the terminal is any of the structural units represented by the following (d1) to (d6) (however, when the unit is represented by (d4) or (d5), (d4). Alternatively, it also has a unit represented by (d5)), a structural unit derived from a monomer copolymerizable with a divinyl aromatic compound or a monovinyl compound, or a structural unit derived from a terminal modifier or a chain transfer agent.

(In the formula, R ² represents an aromatic hydrocarbon group having 6 to 30 carbon atoms.)

(In the formula, R ³ indicates an aromatic hydrocarbon group having 6 to 30 carbon atoms, and R ⁴ indicates a hydrogen atom or a hydrocarbon group having 6 to 30 carbon atoms.)
―YOZ (d3)
(In the formula, Y represents an aromatic hydrocarbon group having 6 to 52 carbon atoms substituted with an unsubstituted or hydrocarbon group having 1 to 12 carbon atoms, and Z represents an aliphatic hydrocarbon group having 1 to 30 carbon atoms. Alternatively, it indicates an aromatic hydrocarbon group having 6 to 52 carbon atoms, which is unsubstituted or substituted with a hydrocarbon group having 1 to 12 carbon atoms.)

(Here, R ⁵ indicates a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms, R ⁶ and R ⁷ indicate a hydrocarbon group having 1 to 18 carbon atoms, and R ⁸ indicates a hydrogen atom or a methyl group. .)

(Here, R ⁹ is a hydrocarbon group having 1 or 2 or more alicyclic hydrocarbon rings and having 4 to 16 carbon atoms.)
The structural unit (a) is contained in an amount of 2 mol% or more and less than 95 mol%, and at least a part of the structural unit (a) is a vinyl group-containing structural unit (a1) represented by the following formula.

(In the formula, R ¹ represents an aromatic hydrocarbon group having 6 to 30 carbon atoms.)
At least a part of the other structural unit (a) is a structural unit constituting the structural unit (d), and the molar fraction of the vinyl group-containing structural unit (a1) with respect to the sum of the structural units (a) and (b) is A copolymer rubber having a number average molecular weight in the range of 0.02 to 0.8 and having a number average molecular weight of 300 to 100,000. The copolymer rubber according to claim 5 , wherein the structural unit (A1) has a number average molecular weight of 300 to 100,000. A crosslinked rubber composition comprising the copolymer rubber according to claim 5 or 6 and a filler, wherein the copolymer rubber has a crosslinked structure.